Licenses are granted by copyright holders to grant exceptions of copyright law to users for a work. Works can be made available under a single license, but the copyright holder has the option of making their work available under any number of licenses. Copyright symbol. ...

Use in free software

Dual licensing is used by the copyright holders of some free software packages advertising their willingness to distribute using both a copyleft free-software license and a non-free software license. The latter license typically offers users the software as proprietary software or offers third-parties the source code without copyleft provisions. Copyright holders are exercising the monopoly they're provided under copyright in this scenario, but also use dual licensing to discriminate the rights and freedoms different recipients receive. This article is about Free Software as defined by the sociopolitical Free Software movement; for information on software distributed without charge, see freeware. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Proprietary software is software that has restrictions on using and copying it, usually enforced by a proprietor. ... Copyright symbol. ...

Such licensing allows the holder to offer customisations, early releases, generate other derivative works or grant rights to third parties to redistribute proprietary versions all while offering everyone a free version of the software. Sharing the package as copyleft free software can benefit the copyright holder by receiving contributions from users and hackers of the free software community. These contributions can be the support of a dedicated user community, word of mouth marketing or modifications that are made available as stipulated by a copyleft license. However, a copyright holder's commitment to elude copyleft provisions and advertise proproprietary redistributions risks losing confidence and support from free software users.[1][2] Hackers are sometimes portrayed as mysterious and strange. ... Word of mouth (WOM) is the passing of information by verbal means, especially recommendations, but also general information, in an informal, person-to-person manner, rather than by mass media, advertising, organized publication, or traditional marketing. ...

A second use of dual-licensing with free software is for license compatibility, allowing code from differently licensed free software projects to be combined or to provide users the preference to pick a license.

Examples of dual licensed free software are:

• Asterisk PBX
• Berkeley DB by Sleepycat Software
• eXo Platform
• Internet Communications Engine
• Mono
• Mozilla Application Suite by the Mozilla Foundation
• MySQL by MySQL AB
• Perl
• Qt by Trolltech
• Sendmail

Asterisk is a free software / open-source software implementation of a telephone private branch exchange (PBX). ... Berkeley DB (DB) is a high-performance, embedded database library with C, C++, Java, Perl, Python, Tcl and many other language bindings. ... Sleepycat Software makes Berkeley DB, the most widely used open source developer database in the world with over 200 million deployments. ... The Internet Communications Engine, or Ice, is a Remote Procedure Call and object middleware system developed by ZeroC and dual-licensed under the GNU GPL and a proprietary license. ... Mono is a project led by Novell, Inc. ... The Mozilla Application Suite (originally known as Mozilla, marketed as the Mozilla Suite, and code named Seamonkey) is a free, cross-platform internet suite, whose components include a web browser, an e-mail and news client, an HTML editor, and an IRC client. ... The Mozilla Foundation is a non-profit organization that exists to support and provide leadership for the open source Mozilla project. ... MySQL is a multithreaded, multi-user, SQL Database Management System (DBMS) with more than six million installations. ... MySQL AB (founded 1995) is dual headquartered in Uppsala, Sweden and Cupertino, California, USA. The company is the creator and owner of MySQL, a relational database management system. ... Perl, also Practical Extraction and Report Language (a backronym, see below) is a dynamic procedural programming language designed by Larry Wall and first released in 1987. ... In computer programming, Qt is a cross-platform graphical widget toolkit for the development of GUI programs. ... Trolltech (formerly known as Quasar Technologies) is a computer software company from Oslo, Norway. ... Sendmail is a mail transfer agent (MTA) that is a well known project of the open source and Unix communities and is distributed both as free software and proprietary software. ...

In proprietary works

Dual licensing can also be used to segregate a market. By splitting people into categories such as home users, professional users, and academic users, copyright holders can set different prices for each group. Proprietary software is software that has restrictions on using and copying it, usually enforced by a proprietor. ...

External links

• Dual Licensing Advisory from OSS Watch
• Article "The Dual-Licensing Model" by Don Marti
• Article "Dual Licensing: Having Your Cake and Eating It Too" by Philip H. Albert
• Article "Dual-Licensing Open Source Business Models" by Heather Meeker
• Article "How to use open source as a power marketing tool" by John Koenig
• Paper "Dual Licensing in Open Source Software Industry" by Mikko Välimäki
• Dual Licensing Strategies from Open Source Law Blog
• Dual Licensing Schemes
• How dual licensing works
• SOE launches dual licensing program
• GPL violations